The reaction of 2,1-benzisothiazoline-3-thiones with acetylenic reagents

Abstract

N-Methyl-2,1-benzisothiazoline-3-thione reacts with acetylene esters to form o-iminobenzoquinone methides which either form diazocines 2 by head-to-tail dimerisation, or react further with the acetylenic ester forming diadducts. With phenylacetylene a 1,2-difhiolo[2,3-b]2,1-benzisofhiazole structure is obtained by rearrangement of an initial adduct. Related thiones and acetylenes react similarly but in poorer yields. The crystal and molecular structures of the diazocine were determined by single crystal X-ray diffractometry techniques. The compound crystallizes in space group [Formula: see text] with unit cell dimensions a = 7.9465(10), b = 13.6421(14), c = 13.9183(18) Å, α = 82.38(1), β = 83.67(1), γ = 85.77(1) deg, and Z = 2. The structure was solved by direct methods and refined to an R value of 0.056 for 3037 observed reflections. The structure consists of molecules of 2a which have an approximate C2 axis passing through the center of the eight-membered ring. Deviations from true symmetry result from internal ring strain, lone pair–lone pair repulsions, and packing effects.